Protective arrangement for electric power lines



March 27, 1934.

R. 07 KAPP ET AL 1,952,258

PROTECTIVE ARRANGEMENT FOR ELECTRIC POWER LINES Filed May 23, 1929 10 Sheets-Sheet 1 March 27, 1934. R O KAPP AL 1,952,258

PROTECTIVE ARRANGEMENT FOR ELECTRIC POWER LINES Filed May 23, 1929 10 Shee eet 2 March 27, 1934. R Q KAPP r AL 1,952,258

PROTECTIVE ARRANGEMENT FOR ELECTRIC POWER LINES Filed May 23. 1929 10 Sheets-Sheet 3 N TH lm/erzfomy Aim/ rey March 27, 1934. R. o. KAPP El AL PROTECTIVE ARRANGEMENT FOR ELECTRIC POWER LINES Filed May 23, 1929 10 Sheets-Sheet 4 fi s E u w m E 3% 5 LI nlb mnn/ ovm lfllfia AV QQWIII. v a E QUI- H.I H o o hung T- H \z E 9% v k w a 4 w 5.... Em 1 ..l L 0 Ma 30 Q? M March 27, 1934. R 0 KAPP r A 1,952,258

PROTECTIVE ARRANGEMENT FOR ELECTRIC POWER LINES Filed May 23. 1929 10 Sheets-Sheet 5 A Tia/hey March 27, 1934. R, Q KAPP r AL 1,952,258

PROTECTIVE ARRANGEMENT FOR ELECTRIC POWER LINES Filed May 23, 1929 1o Sheets-Sheet e l9 01 2 2; and C. 6'. C'arroZlev-s After-Trey March 27, 1934. R. o. KAPP ET AL PROTECTIVE ARRANGEMENT FOR ELECTRIC POWER LINES Filed May 23, 1929 10 Sheets-Sheet 7 UUUU UUU [71 V67? Zb/nsj R0./7 8, 8 7d Ciafarka zem March 27, 1934. R Q KAPP Er AL 1,952,258

PROTECTIVE ARRANGEMENT FOR ELECTRIC POWER LINES Filed May 23. 1929 10 Sheets-Sheet 8 Zvvenfar-S: ja lnijj 0/210 Znc (lea-j 6607a farroflevxs 5 ii v ww March 27, 1934. R. o. KAPP- ET AL PROTECTIVE ARRANGEMENT FOR ELECTRIC POWER LINES Filed lay 23, 1929 CBI I INYENTdRS REGINALD OT-m KA PP CHARLES GEORGE CARROTIIERS 10 Sheets-Sheet 9 March 27, 1934. R. o. KAPP El AL 1,952,258

PROTECTIVE ARRANGEMENT FOR ELECTRIC POWER LINES Rah app 77i CCzrrollers 5 y M W o Y Patented Mar. 27, 1934 UNITE-D STATES.

PAT-ENT- orrics PROTECTIVE ARRANGED/IENT FOR ELEC- TRIC POWER, LINES land, a Swiss company Application May 23, 1929, Serial No. 365,527 r in Great Britain May 23, 1928 23 Claims. (Cl. 1'75294) The present invention relates to improvements in or relating to protective arrangements for electric transmission systems whether, for example, for power linesin an overhead transmission sys- 5 tern or for cables in a high tension underground systemand more particularly concerns improved arrangements for clearing faults on a line orcable with a minimum amount of disturbance to the system of which the line or cable forms a part, the general object of such arrangements being to isolate only the faulty section while the.

remainder of the system remains in service.

The principal object of the invention is to provide reliable means by which the controlling ap- 5 paratus may be made highly and reliably selective, so as to eliminate the risk of sections other than the section or sections which require to be cut out being affected and may be generally in dependent of time lag devices or marginal devices ifor their operation.

Broadly speaking the invention is characterized in that, in the event of a fault occurring in a section, current flowing over a pilot wire is reduced to zero or changed to a current having a ,.particular value, direction or other characteristic which differs from the current flowing in the pilot wire if the fault occurs in some other section of the system.

One of the features of the present invention concerns the provision of switching devices at eachend of a section of a system which devices respond to current flowing in the section, 1. e. either residual current or balanced current, and are arranged in certain circumstances, when a fault occurs or under normal running conditions and, when the current flowing in at one end is the same as the current flowing out at the other to cause current to flow over a pilot wire or like equivalent circuit. The pilot Wire is arranged in 0 a circuit which includes controlling devices at one or both ends which controlling devices are adapted to respond to eifect the isolation of the section when the flow of current through the pilot wire circuit is interrupted or changed to a ourren't having a predetermined characteristic such as direction or value when current flowing into the section at one end diifers in value and/or direction from the current flowing at the other end.

A' further feature of the present invention is' the provision of'controlling arrangements in conjunction with the pilot wire circuit by which interruption of current flowing over the pilot wire circuit in certain circumstances (i. e. on a fault occurring) is adapted to eifect the cutting out of the section with which it is associated.

Another feature of the present invention, which is allied to the two features already mentioned, is that the controlling arrangements are arranged in such a way that the absence of current flowing in the pilot wire or the flow of current in the pilot wire having a predetermined characterizing feature differing from that of the current flowing in other circumstances (i. e. on a, fault occurring in another section) is adapted to cause a circuit to be closed for the purpose of effecting the cutting out of the section. The controlling arrangements to attain the above results may be conveniently in the form of a duplex, quadruplex or multiplex signalling arrangement as'used in telegraphy. In certain multiplex signalling arrangements as used in telegraphy it isnecessary to use synchronously moving parts and, while it is possible to use such parts for protecting power lines, it is probably undesirable as they will re quire more maintenance and are more likely to get out of order. For-this reason it would be preferable to use multiplex signalling arrangements of the type in which the various channels correspond to different frequencies of alternating current and this term multiplex signalling, it must be understood covers carrier current arrangements and voice current signalling arrangements. It would also be apparent that while the term pilot wire is used it is capable oi. being'replaced by any equivalent circuit, for in-' stance by a wireless transmitting and receiving arrangement or by superimposed circuits as well as simple direct wire circuits; Further, the direct wire circuits may run alongside the cable or could be lines running, for instance to a central station so as to make use of the wire already in existence, or they could be lines normally used for some other purpose.

Further features of the invention include arrangements for varying one characteristic of a quadruplex signalling system independently of the variation of a second characteristic, such variation being arranged to effect the cutting out of a' faulty section. The variation of the other characteristic could be usedforcutting out a second section running between the same two points as the first section or could be used for the insertion of a time lag control if the principal control fails for any reason, or it could be arranged for sending controlling currents for different kinds of faults from those for which the variations of the first'characteristic are used or for sending signals.

Similarly the invention contemplates as a further feature the cutting out of a faulty section tion.

by controlling currents transmitted over any one channel of a multiplex signalling arrangement.

A further feature of the present invention concerns the provision of current or power measuring devices located at each end of a section of the system which devices are arranged to control the cutting out of the section if they are not actuated in the same manner.

It may happen that the circuit-breakers fail to operate when tripped to isolate the faulty section and the invention therefore contemplates the provision of a time lag device which would operate after a short delay to operate the circuitbreaker at the end of the section which is adjacent to the faulty circuit-breaker so as to ensure the isolation of the fault even in this case.

One of the advantages of employing controlling rrangements operating over the pilot wire as covered by the preceding features is that if a fault develops in such circuits due, for instance, to the pilot wire being broken, it is possible still to efiect the automatic isolation of the section and a further novel feature of the invention therefore relates to the provision of a section of cable for electric power transmission systems in which the pilot who is embedded in the cable, such pilot wire being connected to controlling devices which are influenced by current flowing over the pilot wire so that they will not prevent the automatic isolation of the section when the pilot wire circuit is broken. Similarly in over head transmission lines the invention contemplates utilizing an insulated pilot wire arranged in the earthing wire instead of one of the strands thereof, such pilot wire being provided with siinilarly arranged controlling devices.

In certain cases it is desirable that an alternative protection should be provided in case the pilot wire should break and a further feature of the invention contemplates providing for this by arranging that while direct current of one value flows over the pilot wire when a fault occurs in another section direct current of a different value news over the pilot wire when the fault occurs in the section but if for any reason current should fail to flow then the trip circuits of the circuitbreakers at the ends of the section could be placed out of action and replaced by a time lag protec- It may happen, however, that the pilot wire breaks at the moment of a fault in which event it could be arranged that the time lag is only brought into operation after a delay so as to permit the switches in this case to operate before the time lag becomes operative.

It is believed that a further novel feature of the invention relates to the provision of two protecting means one of which is normally in action and enables the section to be selectively and immediately isolated on the occurrence of a fault in the section and a second protecting means of a cruder nature such as time lag devices which are brought into action automatically in the event of the first protecting means becoming faulty for any reason.

Again, due to the invention providing such a reliable means for cutting out a faulty section, that is to say, means which are both highly selective and operate immediately to isolate a sec 'tion, it is possible a complete transmi sion system still to employ time lag devices or devices dependent upon a time element for protecting some of the sections with a consequent reduction of cost and the invention therefore contemplates provision of a complete system having protecting arrangements of the different kinds mentioned for protecting different sections. It will be clear that the effect of introducing sections protected in such a way as reliably to ensure the cutting out of a faulty section only into a system which is protected by a cruder form of protection will make the cruder form of protection relatively more efficient. Except where current or power measuring devices are used exclusively for the protection of a section the invention contemplates the employment of directional relays which may be operated by either residual or balanced current. In the latter case of course the relays would be operated whenever current flowed on the line in a particular direction, while in the former case the relays would be operated only when a fan t occurred and caused residual currents to flow in a particular direction. The residual current is the algebraic sum of the instantaneous values of the currents flowing in the different conductors of a power line. The currents in the power line are balanced when the residual current is Zero.

These and other features of the invention will be better understood by referring to the following description having reference to the accompanying drawings which show by way of example illustrative embodiments of the invention.

Figures 1 and la show a complete transmission system including overhead transmission lines and underground cables together with protecting arrangements suitable for isolating faults according to the individual conditions of the various lines.

Figure it shows a section of a stranded earthing wire with interlocked strands having an insulated pilot wire forming one of the strands for use with overhead transmission lines when en1- ploying protective arrangements according to the invention.

Figure 10 shows a section of a cable having a pilot wir embedded therein. It is possible by means of the present invention to utilize a pilot wire in this position for protective purposes.

Figure 2 shows an arrangement for controlling the cutting out of a faulty section over a pilot wire circuit and for cutting out an adjacent section under the control of time lag devices.

Figure 2a shows the use of a power balanced relay.

Figure 3 shows an arrangement for controlling the cutting out of a faulty section by opening circuits over a pair of pilot wires and also for cutting out an adjacent section under the control of time lag devices.

Figure l shows an arrangement for controlling the cutting out of a faulty section by reducing the current in a single pilot wire to zero or by breakage of the pilot wire, the controlling arrangements at each end of the pilot wire being identical.

Figure 5 shows another arrangement for controlling the cutting out of a faulty section reducing the current in a single pilot wire to zero, in which the circuit controlling arrangements resemble those employed in opposed duplex signalling in the art of telegraphy.

Figure 6 shows another arrangement somewhat similar to that shown in the preceding figure in which the circuit controlling arrangements resemble those employed in that kind of signalling known as combined duplex signalling in the art of telegraphy.

Figure 7 shows the application of a low voltage release relay to arrangements in which the opening of the pilot wire circuit in certain circumstances effects the isolation of the section.

Figure 8 shows circuit controlling arrangements employed in conjunction with a pilot wire, which resemble those employed in quadruplex signalling in the art of telegraphy; one channel being employed for controlling the cutting out of one section, while the other channel is employed for the cutting out of another section running between the same points.

Figure 9 shows a modification of the arrangement shown in Figure which is applicable to sectionsin which power is supplied from one end only.

Figure 10 shows in greater detail the circuit arrangements of the arrangement shown in the preceding figure.

Figure 11 shows circuit controlling arrangements-resembling those employed in quadruple}; signalling in which one channel is employed for protecting the section from faults of the kind in which the earth currents are suiiiciently great as to change the direction of current flow or substantially'arrest the flow of current at one end, i. e. when the differences between t .e currents flowing into or in the section at one end and out at the other are very considerable, while the other channel iseinployed for protecting the section from faults of the kind in which the leakage is comparatively small as in underground cables d a; is determined by the different manners in which ment shown in Figure 9 to quadruplex working to enable two sections running between the same points to be protected by a single pilot wire.

1 Referring to Figures 1 and la which show a complete transmission system of three-phase high tension alternatin current comprising the overhead transmission lines 1, 2, 3, 4., 5, 6, 8, 9, 12 and' the underground cables 7, 10 and 11. The lines 1, 2, 3, 4 and 5 are in'tandem while the lines 657, 8, 10, 11,12 form a ring main interconnected with the tandem lines at station while the line 9 connects a station J to the ring main at station I.

It will be assumed that each of the stations A, B, C, D, E, F, G, I, K and ii are generating stations adapted to supply power to the system or take power from the system according to whether the local demand for power below or above the amount generated locally, while station J 'is purely a power consuming station.

While Figures 1 and In only show the protective apparatus in a very schematic manner, details of the apparatus and its manner of operation will be described more particularly with reference to Figures 2-l1 of th accompanying draw- The transmission lines 1 and 2 between stations A and B, and B and C respectively are provided with both a pilot wire represented by the reference 6 at the left-hand end and 7 at the right-hand end, and an earthing wire EW which are run on separate lines. The arrangement employed for protection will correspond at station E to that shown and described with reference to Figure 2; at station A the arrangements will be identical with those shown at the right-hand side of Figure 2except that the positive pole of battery 18A will be connected direct to earth. The protecting arrangements at the right-hand side of station C willbe similar to those at the left-hand. side of Figure 2, except that the coil 143 will control contacts arranged similarly to thosecontrolled by coil 3113 of Figure 3 so as to open the pilot wire circuit when energized and not to close it. The transmission lines 3 and l are provided with two pilot wires forming insulated strands "of the stranded earthing wire similar in section to that shown in Figure lb, except that there are two cores instead of one in the centre. "The protective arrangements shown in Figure 3 are especially adapted to permit of the pilot wires being so arranged that in the event of the earthing wire being damaged and the pilot wires broken the circuit-breakers can still operate to isolate the faulty section. At station I) the apparatus is the same as that between the leads 24 and 25 and the leads 26 and 27 of Figure 3; while at the right-hand side of station C the apparatus is the same as the apparatus at the right-hand side of the apparatus between the leads 24 and 25 and the leads 26 and 27 of Figure 3, except that the coil 32D controls contacts similar to the contacts 173 controlled by coil 1513. At the left-hand of station C the apparatus is the same as the apparatus at the lefthand side of the apparatus between the leads 24 and and the leads 26 and 2'? of Figure 3, except that the coil 31D and its contacts are omitted or are controlled in a difierentmanner.

The transmission line 5 is provided with a single pilot wire forming an insulated strand of the stranded earthing wire, shown in section Figure 1b. The strands are interlocked, as shown, to prevent the insulation being worn away due to the normal contractions and expansions of the cable under temperature changes or varying strains. The protective arrangements would then conveniently take the form shown in Figure'4 as in this case also the circuit-breakers can still operate to isolate the section 5 if faulty, even although the pilot wire is broken. It will be understood that the protective arrangements at the right-hand of station F would be the same as the protective arrangements shown'more in detail at the left-hand side of Figure 5 and the protective arrangements at the left-hand of station F would be the same as the protective arrangements shown more in detail the the right-hand side of Figure 4.

Station F is on the ring including overhead transmission lines 6, 8, 12 and cables '7, 10 and 11. Transmission line 6 is similar to transmission line 5 and t .e pilot wire 31 again forms an insulated strand of the stranded earthing wire, for instance as shown in Figure 1b. In this case it has been found that further advantages could be obtained by arranging controlling arrangements so that not only are the controlling arrangements at the two ends of the pilot wire balanced but also the circuit as regards the controlling devices at each end are balanced. Such an arrangement is shown in detail in Figure 5 of the drawings. arrangements at the right-hand side of station F corresponding to the protecting arrangements are shown more in detail at the left-hand side of Figure 5, while the protecting arrangements at the left-hand side of station G correspond to the protecting arrangements shown more in detail at the right-hand side of Figure 5. Y

The stations G and H are linked together by an underground cable having a pilot wire embedded therein. Such a cable for the three-phase transmission system described may conveniently have a section such as that shown in Figure 10. In this case it is necessary that the protecting arrangements should be such as to permit the circuit-breakers to isolate the section even although The protecting in the event of 'a fault occurring in the cable the pilot wire is itself broken or damaged. A convenient form of protection in these circumstances is shown in Figure 6 and it will be understood that the protective arrangements at the left-hand side of Figure 6 show more in detail the protective arrangements at the right-hand side of station G while the protective arrangements at the left-hand side of station H are shown more in detail at the right-hand side of Figure 6.

The stations H and I are interconnected by two separate three-phase transmission lines and in order that only a single pilot wire forming an insulated strand oi a stranded earthing wire may be used for the protecting of both lines an arrangement such as that shown in Figure 8 should be used. This arrangement shows a quadruplex signalling arrangement for protecting the power lines. The protective arrangements for both lines are represented by rectangles in the right-hand side of station H and the left-hand side of station I and are shown more in detail in the 1eit-hand and right-hand sides of Figure 8 respectively It may happen that current is fed to a nal station where there is no generating apparatus. Such a condition represented by station J. If a fault occurs then current can only be fed to the fault from station I. To meet these conditions protective arrangements, such as are shown in Figures 9 and 10, should o Jv-l although they are also capable being used in other circumstances as will be later. The protective arrangements at the "upper righthand side of station I and station J are shown more in detail in the left-hand sides Figures 9 and 10 and the right-hand of Figures 9 and 10 respectively.

Underground cables are normally subject to two kinds of faults as distinct from the kind to which overhead transmission lines are subject, namely faults of a serious character involving heavy currents to earth and faults in the nature of leaks often termed incipient faults. These latter faults cannot be dealt with by the protective arrangements so far described and the cable 10 running between stations K and is protected from both kinds of faults by protective arrange ,ments in these stations, such as are shown more :in detail in Figure 11.

Two cables 11 are provided for interconnecting stations K and L, which cables are protected only by a single pilot wire embedded in one cable. 'The protective arrangements in such a case would conveniently be of the kind-described with reference to and shown in detail in Figure 12.

The transmission line 12 being the only remaining section of the system for interconnecting station L with station E can be protected by time lag devices which are well-known in the art and are represented by dash-pct relays. the fact that all other sections of the system are selectively and immediately isolated by means of the protective arrangements, according to the invention it is clear that if a fault occurs which is not immediately cleared the fault will be on the transmission line 12 which therefore need only be protected in a much cruder manner and the expense of pilot wires can for this particular section be avoided.

Figure 2 shows in detail the protective ar ang r c merits between stations A and B, and B and C. The electric power line 2 between the stations power line 1 between the stations A and B is connccted to the bus-bars 3B and 3A via the circuitbrealrers 2B and 1A respectively. The control of the circuit-breakers for the section between stations A and B is eiiectcd over a single pilot wire '2', while control of the circuit-breal zers between the stations B and C is effected over the pilot wire 6. The control is effected by means of the directional protective relays 9C, 813, 9B and 8A. These relays may either be leakage relays responsive to residual currents as illustrated in Figure 2, that is to say they are only energized when the vectorial sum of the currents flowing in the three phases of the transmission line is other than zero indicating that there is a leakage to earth or, the relays may be power relays responsive to balanced currents as illustrated in Figure 2a. If directional relays responsive to balanced currents employed, then as long as conditions are normal no current flows through the relays or the current how is in such direction as to operate the directional relay at one end of the line only but if fault should develop the current flow would be such as to operate both directional relays. Included in the circuit of the pilot ers 1B and 20 respectively, circuit of the pilot wire 7 are coils 13B 12A associated with the circakers and 1A respectively. The so "cc of electrical energy for operating the trip s obtained from the batteries 19C, 18B, 193, ion, he batteries at station B forming a single battery split to two parts which are connected at the junction to earth or to return pilot wires by way of the coils 15B and 148 respectively of time lag relays, which relays serve to close contacts 17B and 163 a predetermined time alter they -:ave been energized, which predetermined time s preferably adjustable. As station A is a terminal station and as the purpose of the time relays, as will be described, is to close a point in the pilot wire of an adjacent section, it will be appreciated that no time lag relays are requi' 1d at this station. At station C the battery 196 is connected to a time lag relay 14 C which operates to open contacts in th circuit of the pilot wire 26 as in this case the protection arrangements diITer for reasons which have already ceen descri ed. The time lag relay 390 which controls the -lot wire 6 controlled in the circuit of the trip coil 38C of the circuitbreaker .WC (Figure 3) to close contacts 170 in case the trip coil 38C fails to eiTectiVely trip the circuit-breaker 47C.

In order to explain the operation of the protection arrangements as illustrated in Figure 2, it will be supposed that earth fault occurs on a portion of the line 1. Current will then flow through relay 9B in such a direction as to cause it to operate contacts 113 and through the relay 8A at the other end of the line 1 in the opposite direction so as to operate this relay also. Consequently a circuit is completed from earth, time coil 143, battery 1933, trip coil 133, contacts 111%, pilot wire 7, contact 10A, trip coil 12A, battery 18A to earth. If station A had not been a terminal station the circuit would have included at station A a time lag relay similar to coil 15.8 (at station B) arranged to operate contacts similar to 173 in the circuit of the pilot wire leading to the next station. If everything is in order the energization of the trip coils in this circuit causes circuit-breakers 2B and 1A to trip so that the fault is duly cleared. In case for some reason the circuit-breaker 23 should fail to open after a short time interval contacts 163 would be closed by the time lag relay 14B and a circuit would then be completed over the pilot wire 6 as follows: earth, time lag relay 1513, battery 18B, trip coil 12B, contact 1 6B, pilot wire 6, contact 116, trip coil 130, battery 190', t me lag relay 14C, to earth. In this circuit trip coils 13C and 123 would be energized causing the circuit-breakers 2C and 115 to trip so that lines 2 and l are both out out, that is to say the faulty section and an adjacent section are cut out in this eventuality. It will be appreciated that although there previously have been a fault current flowing through the directional relay 8B due to the fault under consideration, this current is the wrong direction to operate this relay although it will have operated relay 96 at the other end of the line 2. This arrangement ensures that the circuit-breakers will only come out in the section on which the fault has occurred as it is clearly undesirable that more sections should be rendered dead than is absolutely necessary. The principal novel feature shown in this figure is the arrangement of the time lag devices by which, in the event of a circuit-breaker failing to trip, a circuit is completed to trip the circuit brealiers of an adjacent section.

Figure 3 shows a modified arrangement in which the feature of absence of current on the pilot wire of a faulty section is embodied.

In Figure 3 the electric power line i connects station E to station D while the power line 3 connects station D to station C. he power lines 4 and 3 are connected to the bus-bar 231) by way of the circuit-breakers 45D and 4613 re- .spectively, while the trip coils for the circuitbreakers 45D and 46D have the references 38D and 3913. The power line 3 is connected to the bus-bar BC by way of the circuit-breaker 4:70 which circuit-breaker is controlled by the trip coil 380, while the power line 4 is connected to the bus-bar 23E by way of the circuit-breaker 46E which is controlled by the trip coil 39E. Directional leakage relays 30E, 29D, 30]), 420 are provided as in Figure 2, the relays in these cases having changeover contacts. Use is also made of relays 36D, 37D, 37E and 41C which are now normally energized over the pilot wires 24, 25, 26, 27 and serve to hold open their associated contacts. Thus the circuit for coil 37]) extends from earth, battery 34D, relay 37D, pilot wire 26, normally closed contacts of directional relay 42C, normally closed'contacts of time lag relay 14C, battery 44C to earth. Instead of an earth connection a third pilot wire can be used connecting the points to which earth is connected, which will be "eadily appreciated. As long, therefore, as normal conditions are obtained all the pilot wire relays, 36D, 37D, 41C, 37E will be kept energized and the circuit for the trip coils 39E, 38D, 39D, 380 will be kept open. that a fault occurs on line 3 directional relay 30D will operate to break its lower contacts and to close its upper contacts. The effect of this is to open the circuit of pilot wire relay 41:3 and prepare a circuit. for the trip coil 399. Moreover at the same time directional relay 420 will have been operated to open the circuit of pilot wire relay 37D and to prepare a circuit for the trip coil 38C of the circuit-breaker 470 at station C. Owing to the release or pilot wire relay 37D a circuit is now completed as follows: positive pole of battery 3333, trip coil 39D, upper contacts of directional relay 36D,

Assume new contacts of pilot wire relay 37D, time lag coil 311) to negative pole of battery. Accordingly circuitbreaker 4613 is operated. Circuit-breaker 470 at the other end of the line is also operated clue to the energization of tripping coil 38C in the circuit, negative pole of battery 2330, trip coil 38C, upper contacts of directional relay 420 closed contacts of pilot wire relay 410, time relay 33-5 (Figure 2) to positive pole of battery 33C. The purpose of the time lag coils is exactly the same as the purpose of the time 1a coils 14B and 1533 described in connection h That is to say, in the case of either or 47C failing to operno circuit-breaker 46E or 1B will operate to isolate the line 4 as well as the line 3 or the line 2 well as the line 3, dependin upon which circuit-breaker has failed. Thus if upon occurrence of a fault on line 3 the circuit-breaker 46D fails to open after a time lag, the current flowing in the tripping circuit, which includes the coil 3iD, causes the contacts controlled by that coil to open, whereby the pilot wire coil 37E at station E will be die-energized and since the directional relay 39E will have closed its upper contacts on the occurrence of a fault the tripping circuit for the circuit-breaker 46E will be completed when that circuit-breaker opens.

Actually in this case there are two pilot wires and depending upon the direction of current flow the breakage of a pilot wire will cause a circuit-breaker to trip in either of the following circumstances: i. e. in the case when directional relays responsive to residual currents are used and a fault occurs anywhere in the system and in the case when directional relays responsive to balanced currents as illustrated in Figure 2A a e used, irrespective of whether a fault occ" s in the system or not, the reason being that in this latter case one of the directional relays will always be energized. In the first case assuming that pilot wire 27 breaks and a fault occurs in line 4, then owing to current flowing to the fault from station C directional relay 420 will operate and pilot wire relay 410 will deenergiae thereby completing a circuit for trip coil 38C causing circuit-breaker 47C to trip. In the second case one of the directional relays sec or 30!), wfll always be operated and so a similar circuit wil be completed. On the other hand if pilot wire 26 breaks instead of pilot wire 27, then in the cases considered neither circuit-breaker sen nor MC will trip as the direction of current towards 4 will be such that directional relay 426 will operate and there will be an opening in the circuits of the tripping coils of each circuit-breaker.

The advantage of this latter construction is that not only is the line on which the fault occurs immediately selected and cut out, but even if the pilot wires are themselves damaged the circuit-breakers will still be operated.

The arrangement shown in Figure 4 possesses all the advantages of the last mentioned construction while employing only a single pilot wire.

Referring now to Figure 4 the stations E and are connected by the electric power line 5. In this case the directional relays 50, 51 are arranged with their lower contacts in series with the pilot wire 52 earthed batteries 53 and 54'. At opposite ends or" the pilot wire on the pilot wire side of each directional relay, pilot wire relays 55 and 56 respectively are connected between the pilot wire 52- and earth. The upper contacts of the directional relays are con ected in the circuit of the trip coils 57 and 58 respec tively. These circuits in both cases include contacts normally held open by the respective pilot wire relays as well as batteries 59 and 60 respectively. The battery 59 could be the s me as battery 53, and battery 60 the same as battery 54. It will be noted that under the circuit conditions shown the pilot wire relay 55 is held energized both from i s local battery 53 and from the distant battery 54 over the pilot wire. The pilot wire relay 56 is similarly energized from both batteries. In the case of a fault occurring in any section of the transmission system other than between stations E and F one or other, but not both of the directional relays 50 and 51 will be operated and have its upper contacts closed. If the directional relays are of the type which respond to balanced currents as shown in Figure 2a, then one or other of the directional relays 50 and 51 will always be energized. Consequently one of the pilot wire relays will be dependent for its energization on current flowing over the pilot wire. In the event of a fault in the line 5 then both directional relays will have their upper contacts closed, in which case both pilot wire relays will de-energize, the contacts controlled thereby will close and circuits will be closed for the trip coils 5'7 and 58. By this means the line is isolated. As the pilot wire relays both de-energize, it is clear that if the directional relays are of the type which respond to balanced currents it is immaterial whether the pilot wire 52 is itself broken due to the fault or not.

Hence by means of the present invention the line on which a fault occurs is immediately cut oil irrespective of whether the pilot wire has been damaged or not. As a consequence it is possible by the present invention to embed the pilot wire in the insulation of the power cable without any danger of the protective system being deleteriously affected. Previously it has not been considered desirable to have a pilot wire forming part of the protective system embedded for this reason. In three-phase power cables where the individual conductors are each surrounded by a metallic sheath, the pilot wire could be embedded in the insulation outside the sheaths.

The arrangement just described is a balanced system as regards the controlling arrangements at the two ends of a pilot wire being identical but it was found that further advantages could be obtained by the provision of circuits which were balanced at each end as regards the controlling devices at that end and especially balanced circuits resembling those known as duplex, quadruplex and multiplex arrangements as employed in the art of telegraphy were found to give these advantages, and although certain multiplex signailing arrangements due to the use of normally moving parts are not usually practicable in a number of cases yet there is no reason why they should not be used if found to be suitable in special circumstances.

One arrangement know as opposed duplex will be described with reference to Figure 5. In this figure, l0 and. 71 represent the circuit-breakers, one at each end or" a line 6. Associated with the circuit-breaker 70 is a directional relay 73 in which the armature normally closes contacts 74, although when power is flowing through the line in a particular direction, namely, from left to right, the upper contacts 75 will be closed. In

circuit with the upper contacts is a battery 76. The trip coil of the circuit-breaker is represented by the reference 77 and has connected in series with it contacts '78 controlled by the armature of an electromagnetic relay 79. The electromagnetic relay has windings having a connection made to the inidpointas shown, so that when current is flowing through either the upper or lower half of the windings only the relay will operate, but if current is flowing from the centre-point through both windings then the relay will be deenergized. Associated with the circuit breaker 11 is a similar set of apparatus to that associated with the circuit-breaker 7G and including the directional relay 83 having lower contacts 84 and upper contacts 85, battery 86, trip coil 87, contacts S8 controlled an electromagnetic device 8-9 having its windings arranged similarly to the windings '79. The operation is as follows: In the case of a fault ccurring in any section of the transmission system other than between stations F and G, one or other but not both of the directional relays will have its upper contacts closed while the other will have its lower contacts closed. It will be assumed that the fault is on a section to the right of station so that the contacts 75 are closed and also the contacts 34. In these con ditions circuits may be traced as iollm s: earth, battery 76, contacts 75 to the midpoint of the windings the electromagnet '19. Here the circult divides one half going through the upper half of the said windings, resistance to earth: while the other goes through the lower half of the windings or" the electromagnet 79, the pilot wire 81, lower part of the windings of the electromagnetic device 89, conta ts 84 to earth. The result is that the currents flowing through the upper and lower windings of relay 79 oppose each other and as resistance 80 is so chosen with respect to the remainder of the circuit, that is the pilot wire 81 and the lower winding of the electromagnet 89, that no attraction of the armature of '79 will take place, consequently contacts '78 will remain open, as shown. At the other end of the line the current flowing through the lower winding of electromagnct 89 will. cause its armature to be attracted and consequently contacts 88 to be closed. Trip coil 8? will not be operated in these circumstances due to the resistance of the pilot wire 81. However, if a fault occurs on the line 5 then the directional relay 83 will operate as well as the directional relay '73, contacts 34 will open and 85 close, whereupon new circuit conditions will be set up. As regards current flow over the pilot wire 81, it will be noted that the circuit over this wire can be traced as follows: earth, battery 75, contact 75, lower winding of magnet 79, pilot wire 81, lower winding of electromagnet so, contacts 85, battery to earth. As these batteries are opposed to each other and. will normally be of the same or approxi ately of the same voltage, no current will flow in this circuit and consequently the lower windings of both of the magnets '79 and 89 will be of no effect. At eac" station, however, a circuit is completed through the upper winding which can be traced follows at the left-hand station: earth, battery 76, contacts 75, upper winding of magnet 79 resistance 80 to earth. Consequently the electromagnet '79 attracts its armature and contacts 78 are closed thereby completing a circuit for the trip coil. 7'? and the circuit breaker '76 is tripped. At the other station a similar circuit is completed for the upper winding of magnet 89, Which be traced as follows: earth, battery 86, contacts 85,

upper winding of magnet 89, resistance 82 to earth. Consequently contacts 88 remain closed and a circuit is completed for the'trip coil 87 as follows: earth, battery 86, contacts 85, contacts 88, trip coil 8? to earth. The circuit-breaker '71 is thereupon tripped and the faulty section cut out. If for any reason whilst the contacts 75 were closed the pilot wire 81 became broken or opened then the current flow through the lower winding of magnet'lS would cease and consequently the local circuit through the upper winding of magnet '79 would become effective, con- '70 would be ripped.

tacts 73 would be closed and the circuit-breaker it will be appreciated that exactly the reverse conditions to those described would take place if the current was normally flowing in the opposite direction.

*to the present invention. As this circuit so closely resembles Figure 5 the same reference numerals are used for the same parts with the addition of letter suiiixes and need not therefore be further described. Such an arrangement is shown applied to section G-l-l for protecting the power line 7%.

In Figure 6 instead of a connection being made to the middle point or the winding of 79G it can be made at some other point, for instance in a position in which the number of turns of the winding in the upper part is approximately half the number of turns in the lower half. The same remarks apply to the connection to the in- I termediate point of the winding of magnet 83H.

magnet 89H being connected to earth.

'sidered as being operated with contacts actly twice the amount of current will The pilot wire 816 in this case instead of being connected between the two lower windings of magnets 79G and 89H is connected across the windings of those magnets, the lower winding of In the case of a fault occurring in any section of the transmission system other than between stations G and H, the directional relay 735: will be con- 7561 closed and the directional relay 83H will be considered having its contacts 84H closed. In these conditions circuits may traced as follows: earth, battery 76G, contacts G, upper winding of magnet 79G, resistance 80G to earth, while a branch extends over the lower winding of magnet 79G, pilot wire 81%, contacts 84H, lower winding of magnet 89H, to earth. The value of resistance 80G is such that in this condition exflow through the upper winding of magnet 79G as compared to that flowing through the lower winding and the number of turns the upper and lower windings is so chosen that in this condition there will be no magnetic force on the armature of magnet 79G and contact 786- will rem in open. At the other station contact 8831 will be closed as magnet 89H will be energized. In the event of fault occurring in-the ection G-H then directional relay 33H will operate as well as relay 73G and contact 85H will close. The new circuit conditions will then be as follows: firstly a circuit over the pilot wire can be traced: earth, battery 76G, contacts 75G, lower winding of magnet 79G, pilot wire 81G, battery 86H, contacts 85H, lower winding of magnet 893 to earth. The batteries 76G and 863 are now in ser'es and therefore the current flowing over the pilot the result that the effect of the lower winding of magnet 796 ll preponderate over the effect of the upper winding, contact 786 will be closed, and the trip coil 776% will operate to trip the circuit-breaker At the other end of the line it will be noted that the current through the lower winding of the magnet 89H has also been doubled but at the same time a circuit is comwire will be doubled with pleted as follows: battery 86H, contacts 85H,

upper winding of magnet 89H, resistance 82H, back to battery. l'his current, however, is only equal to that flowing through the upper winding of magnet 798 and resistance 80G and consequently the current flowing through the lower v winding of magnet 89 i preponderates and contacts 88H remain closed. The circuit for the trip coil 87H is therefore completed as follows: battery 86 Z, contacts 855, contacts 88H, trip coil 87H back to battery. It will be noted that in this case, in the event of a fault occurring, current is actually flowing over the pilot wire 816-, whereas in the previous cases described, in the event of a fault occ rring, no current is flowing over the pilot wire 81G. A breakage in the pilot wire would result in the magnets 79G and 89H being operated by the current flowing through their upper windings, that is, if the pilot wire broke at the same instant as the fault occurred. If the fault in the pilot wire occurred with a fault in another section, then the magnet 798% would opcrate and close the contact 78G so that the trip coil 77G would operate and trip the circuit breaker. if the current was flowing in the other direction, that is L-O say contacts SSH and HG were closed, then exactly the same conditions would apply the circuits are somewhat different owing to the two circuits not being perfectly symmetrical ior instance the lower winding of magnet 796- would be energized by current flowing over the pilot wire but in this case the current would extend from earth, lower winding of magnet 89I-i, contacts 85H, battery 86H, pilot wire 81%, lower winding magnet 79G, contacts 74G, to earth. This circuit is equivalent to the circuit considered above in connection with power flow in the reverse direction since the same or similar elements occur, although the order in which the occur is changed. It therefore fol lows that in the event: of a fault occurring in the line 7G the batteries 25G and 861-1 would be connected in series the conditions would be exactly equivalent to those already described.

Where a directional pair of relays, of the type dependent on voltage, is used there is a possibility of the relays failing to act due to the voltage falling to too low a value, for instance as might occur with a fault arising very near a station. On this account it is desirable to have a trip circuit operated by a low voltage release relay. With the arrangement shown, where current normally flows over the pilot wire, it is possible to provide a relay which will open the pilot wire circuit when the voltage falls below a predetermined margin. This voltage would usually be slightly greater than the gross value or" volts with which a directional relay will operate, so that the low voltage release relay would come into operation just before the directional relays become inoperative. The voltage at which the low voltage release relays operate should preferably be less its than the lowest possible voltage that can exist at :any station other than those adjacent to the :fault.

One arrangement in which a l w voltage re-- lease relay may be applied is shown in Figure 7. This arrange .ient consists of a modification. of the apparatus at station G so that instead of the pilot wire 81 in Figure 5 eing connected di-- rect to the lower winding of the relay 89, such. connection is made through contacts and con-- tacts 1G. Similarly the pilot wire 81G is not. made direct to the lower winding of relay 79G- but is made through contacts and contacts. 2G. It will be noted that the circuit of the pilot wire 81 can pass through contact 65% as well 4G to contact 1G, while pilot wire 816 can through contact 7G as well as 5G to contact 26..

In this case power lines 6 and 7 are connected. .by a circuit-breaker AG, the power being fed.

from the busbars through inductive transformers and circuit-breakers BG and CG respectively tothe power lines 6 and "I. It will i assumed that an earth fault occurs on section 7 and that it is of such a nature that the voltage falls so low' that the low voltage release relay LVC de-enei gizes and opens contacts 76, closing contacts 913- and 20G. At contact 20G a circuit is closed forthe tripping coil 216 of the circuit-breaker The circuit-breaker AG is accordin ly tripped and. contacts 22G are closed, thereby completing a. circuit to operate relay 23G as follows: earth, hat-- tery, contact 22G, slow acting relay 23G to earth. After a short interval relay 23G energizes, opens. contacts 4G and 5G and closes contacts At contacts 3G a circuit is completed as follows: earth, battery, contacts 3G, contacts 96, tripping coil l'IG of circuit-breaker CG, relay to earth. Relay 24G is slow to energize but re lay 77G energizes and trips the circuit-brealrer CG. Contacts 5G and 7G open the circuit through the lower winding of relay 7E6: and the pilot wire and consequently as the directional. .relay 83H will be operated and relay 89H is caused to operate, a circuit is completed for the tripping coil 87H over contacts 88H and SEE. Tripping coil 87H operates and con equently the line 6 is isolated at circuit-breakers 71H, CG and AG. It will be noted that when the fault first occurs not only does the low voltage rel ase relay LVC operate but the low voltage release relay LVB will also operate to close contact 256- in parallel with contacts 206 and also to open contacts 66 and close contacts 8G. As contact 46 alsoopened it will be noted that the pilot wire circuit 81 will be open. Due, however, to the delay of the operation of the relay 23G and due to thepresence of the inductive couplings between thepower lines 6 and '7 and the busbars and the opening of circuit-breaker AG the voltage will rapidly rise on the non-faulty side, i. e., power line 6 so that the low voltage release relay LVB will again operate and close contact 6G before contact 4G is opened.

It should be noted that the above arrangement are applicable to any system which operates nonselectively with broken pilot wires. Contacts 1G and 2G could be operated by any current occurring as a result of a fault, for instance in the example shown they are operated by current flowing through the trip coils of the circuit-breakers BG and CG respectively. The contacts 1G and 2G control the circuits th ough the pilot wires 81 and 81G so that in the event of current in a trip coil failing for any reason to trip the switch the pilot wire on the side of the section distant from a fault is operated as was described in connection with Figure 3. It will be noted that contact 2G is a anged to open if circuit-hrealrer BG :fails to operate and contact 1G is arranged to open if circuit-breaker CG fails to operate. This ensures that if the circuit-breakers will not operate to out out the faulty section both the faulty section and the neXt adjacent section will be :isolated.

In any of the circuits herein described it may be arranged that the tripping circuit is only com- ;pleted when either the voltage drops to an agreed fraction of the normal value or when some other distinctive electrical conditon arises which is characteristic of a fault occurring at a short dis- 'tance from the circuit-breaker. This may be :achieved by arranging that a device which oper- ;ates normally to keep the circuit of the tripping coil open, closes contacts in circu.-.t with the tripping coil when the distinctive electrical condion arises. By this means the chances of false :operation when pilot wire is broken can be further reduced.

A description will now be given of protective arrangements controlled over a pilot wire on the lines of the qu drup ex system of telegraphy. Tln the particul ication to be described with reference to F gure 8 two sections of a system :running between stations and I are protected Thy single pilot wire; other applications, some of which will be described later, also come within the spirit of the invention.

Referring to the said Figure 8, 1H and 2l-l represent two lines which require to be protected, while Sl-l represents a pilot wire to which quad- :ruplex circuits connected. At the station H t -i and 21-1, circuit-breakers 4H1 end of the lines 1 :and 4H2 are shown and associated with these cirrcuit-hreakers are the tripping coils 5H1 and 5H2 respectively. At the station I end of the lines the circuit-brealrers and. 412 are shown with their tripping coils fill and 512 respectively. The directional relays 8H and 8I are provided for the line 1H, while directional relays 121-1 and 121 are provided for line 2H. Two batteries. 6H and 7H, and 51 and 71 are provided at each end of the lines 1H and 21-3, the batteries 7H and '71 be- :ing of comparatively low voltage compared with the voltage oi: batteries ll-l and SI, for example, one half of the voltage batteries 5H and 61, while separate batteries 193 and 101 are provided for the purpose of energizing the tripping coils. It will be noted that the connections to the pilot wire at each end include a polarized rliiierential relay or 111 and a differential relay 91-! or 91 respectively.

differential relay 9H and 91 is marginal, 'or in other words, it will operate only when the resultant magnet effect due to the combined effect of the two halves of the windings of the relay exceeds a predetermined value and if the said resultant magnetizing effect falls a certain amount below the predetermined value the relay automatically restores.

Each polarized differential relay 111-1 and 111 is responsive to the direction of the resultant ampere turns produced by currents flowing in its two windings. if the currents flowing in the windings o relay 11?: give a resultant magnetizing flux flowing upwards the relay is restrained, whilst if the currents give a resultant magnetizing current flowing downwards as shown the relay is operated. Similarly the relay lll is restrained by a resultant magnetizing flux flowing upwards but is operated by a resultant magnetizing flux flowing the reverse direction.

The directional relays 81-1 and 81 are normally in the position shown. 11, however, current to which the relay is responsive flows into the line at the end at which the relay is situated the r"- lay moves to the alternative position. The relay, moreover, when in the position show makes battery 7H or 71 only effective, but who in the alternative position makes battery 511 or 61 fective also and bridges a gap in a tri ping circuit.

The directional relays 121-1 1:21 are nor mally in the position shown and are s ilarly influenced by rent flowing in line 2 1 and when a relay 1211 or lI is moved to its alternative position it reverses effective connections of the associated battery 711 or 71 or of the associated batteries 711 or 71 and 611 or A description of the operation of arrange ment shown in Figure 8 will depend upon ther the directional relays are dependent for their operation upon balanced current or upon resldual current. In the case of their being dependent upon balanced current for thei operation to the direction of current flow, which is of course vectorial in the case of alternating current, one of the relays associated with each line would be normally operated. In the case of residual current neither of the directional relays associated with a section of line would be normally operated but in the event of a fault in the section both would be operated, while in the case a fault in some other section one would be operated and one not operated. the circuits to be described where directional relays operated with balanced currents are employed will be the same those which arise when relay operated with residual current used, although occurring somewhat diiierent conditions, it will be Sllfil$l6l1t to describe the circuits for relays of the latt type as the operation in the former case can then readily followed.

If the directional relay 81-1 is operated to open its contacts 361-1 and 371-1 and to close its contacts 381-1 and 391-1 and 4011 and 411-1 and at the same time the adjacent relay is operated to close contacts 521?! and 5311 a trapping circuit is made iron the positive pole of battery 101-1 cugli. contacts 5311, 521-1, 111-1 and e011, and trip coil 51-11 to the negative pole of the battery, with the result that the associated circuitbrealrer 11-11 is opened. Similarly if directional relay 81 and the 91 are both operated at the same time the circuit-breaker 411 is tripped out.

If the directional relay 1211 is operated to open contacts 421-1 and 4311 and contacts i611 and 471 to close contacts 4411 and 4511 and contacts 4.8 1 41911 and contacts 501-1 and 5111 and at the same time the adjacent relay 111-1 is operated to close contacts 541-1 and 5511 a tripping circuit is made from positive pole of battery 1011 through contacts 5411, 553, 511-1 and 561-1, and trip coil 51-12 to the negative pole of the battery, with the result that the associated circuit-breaker 11-12 is opened. Similarly if directional relay 121 and the relay 111 are both operated at the same time the circuit-breaker 412 is tripped out.

In Figure 8 the relays are shown in the posi tions assumed when there is no fault current flowing either in the line 111 or in the line 2H and it will be noted that when the relays are in the positions shown circuits may be traced as follows: from (1) earth, resistance 13H, lower winding of polarized diflerential relay 111-1, lower winding of differential relay 91-1, contacts 4711, 161-1, 371-1, 361-1, positive pole of battery 711 which has its negative pole connected to earth through contacts 421-1 and 4311'. (2) Earth, resistance 131, winding of polarized differential relay 111, lower winding of differential relay 91, contacts 311, 2-01, 211. 201, positive pole of battery 71 which has its negative pole connected to earth through contacts 261 and 271. It will be noted that the pilot wire is connected at station E over the upper windings of relays 1111 and 911 to the positive pole battery ll-1 over contacts 471-1, 4611, 3711, and at station I over the upper windings or" the relays 111 and 91 to the positive pole of batteries 71 over contacts 311, 301, 211 and 201.

The result is t" at no current flows over the i :ough upper windings of 91-1 and 111-1 and the upper windings of relays 91 111, since the batteries 7H and 71 are of equal voltage and are connected in opposition to one another. The current flowing from the batteries 7H and 71 in the circuits above described is insufiicient to operate the relays 9H and 91 and iiows in the wrong direction to operate the relays 111-1 and 111. The relays 91-1, 91, 1111 and 111 therefore remain unoperated.

If a fault occurs on a station to the lei or" station H directional relays 81 and 121 are operated while the directional relays 8H and 1211 remain in the position shown. In these circumstances the following circuits may be traced:

(1) Earth, contacts 331, 321, 231, 221, positive pole of battery 611, battery 61, battery 71, contacts 281. 291, lower winding of relay 91, lower winding of relay 111, resistance 131 to earth.

The circuits for the lower windings or relays 91-1 and 1111 remain as originally described.

In addition there will be a flow of current over the pilot wire 3H in the following circuit:

(2) Earth, contacts 331, 321, positive pole of battery 611, battery 61, battery 71, contacts 281, :91, upper windings of relays 91, 111, pilot wire 31-1, upper windings of relays 111-1 and 91-1, con tacts 4711, 1611, 371-1, 36H, positive pole of battery 71-1, battery 711, contacts 421-1 and 4311 to earth. In this circuit the batteries 61, 71 and 71-1 are connected in series all assisting each other so that the current flowing over the pilot wire and through the upper windings of relays 91, 111, 111-1 and 911 is proportional to the sum or the voltage of these batteries. The direction of current flow in the pilot wire will be assumed to be from positive to negative and in this case would be from station 11 to station I.

The resultant effect as regards each of the relays 911, 111i, 111 and 91 will be considered.

In relay 91-1 the current through the lower winding depends upon the volta e of battery 71-1. The current through the upper winding which has an opposing efiect to the current in the lower winding will be dependent upon the sum of the voltages 61, 71 and 711. The resistances 1311 and 131 are compensating resistances which balance the -esistance of the pilot wire and the upper windings of the relays at the other end of the pilot wire so that th currents will always be in the same proportion to the voltages in the respective circuits and as the voltage of batteries 71 and 711 are approximately equal as also the voltage of batteries 6H and 61, it will be seen that the current through the upper winding of relay 911 will be sufiiciently greater than the current through the lower winding as to cause relay 911 to operate. In

relay 1111 the current through the upper winding will exceed the current through the lower winding exactly the same amount as with relay 91-1 but as the exciting current flows upwards through the lower winding and downwards through the upper winding the current through the upper winding predominates and consequently the direction of resultant magnetic flux will be downwards and relay 1111 will operate.

In relay 111 the current through the upper winding which is of the same magnitude as that flowing through the upper windings of relays 9H and 1111 is proportionate to the sum of the voltages of batteries 71-1, 61 and '71 and flows upwards. The current through the lower winding is proportional to the sum of the voltages of batteries 61 and '71 and flows downwards. Ihe current through the lower winding is proportional to the sum of the voltages of batteries 61 and '71 and flows downwards. It follows therefore, that the resultant magnetic flux will be upwards and proportional to the difference, i. e., the voltage of the battery 7H. Consequently there is no change in the direction or magnitude of the flux in re- .lay 111, therefore relay 111 remains in the position shown.

In relay 91 the currents in the upper and lower windings are exactly the same as the cur rents in the upper and lower windings of relay 111 respectively and consequently the resultant magnetic flux is also unchanged and relay 91 remains in the position shown.

Relay 9H connects contacts 5211 and 5311 but this is without effect as contacts 491-1 and 41211 are disconnected. Similarly the relay 11H connects contacts 5411 and 551-1 but this also is without effect as contacts 5011 and 511-1 are open.

In the case of a fault on a section to the right of station I, exactly similar operations will take place but in this case relays 81-1, 121-1, 111 and 91 will be operated, that is to say, the relays at one station corresponding to those relays at the other station which were operated in the last mentioned case will now be operated in their place as will be readily understood.

In the case of an earth fault on line 111 power will flow to the fault from both station 11 and station 1. Consequently both relays 81-1 and 81 will operate.

Exactly what will happen on line 211 in these circumstances is difficult to forecast and actually it is possible that the earthed current may flow either from station H to station I and so help to feed power to the fault from station I or it may flow from station 1 to station 11 and help to feed power to the fault from station H. While it may happen that actually no earth current at all flows along line 211. In one case relay 1211 will be operated; in the second case relay 121 will be operated, while in the third case neither relays 1211 nor 121 will be operated. Each case will be dealt with in turn.

Firstly with relays 8H, 81 and 121-1 operated and relay 121 unoperated, the following circuits may be traced:

(1) Earth, contacts 491-1, 48H, 39H, 38H, positive pole of battery 6H, battery 6H, battery 711, contacts 4411, 451-1, lower winding of relays 91-1 and 1111 resistance 13H to earth.

(2) Earth, contacts 2'71, 261, negative pole of battery 71, battery 71, battery 61, contacts 221, 231, 301, 311, lower windings of relays 91 and 111, resistance 131 to earth.

(3) Earth, contacts 4911, 4811, 391-1, 38H, positive pole of battery 6H, battery 611, battery 71-1,

contacts can, 455, upper windings of relays 9H and 1111, pilot wire 31-1, upper windings of relays 111, 91, contacts 311, 301, 231, 221, positive pole of battery 61, battery 61, battery '71, contacts 261, 2'71 earth.

The current through the lower winding of relay 91-1 is consequently upwards; in the lower winding of relay 1111 it is downwards and its value is proportional to the voltage of batteries 611 and 7H together. The current through the upper windings of relay 91-1 is downwards, and through the upper winding of relay 11H upwards, while its value is proportional to the sum of the voltage of the batteries 611, 71-1, 61, '21. Consequently the effect of the current through the upper winding of relay 911 will predominate over the effect of the current through the lower winding to an extent sufiicient to cause relay 9H to operate. Also, as the eiiect of the current through the upper winding of relay i111 greater than the effect of current through the lower winding, the resultant magnetic will be upwards and relay 1111 will not operate.

The current through the lower winding of relay 111 will be proportional to the sum of voltage of the batteries 61 and 71 and its direction will be upwards. As the current through the upper winding is downwards but reater, being proportional to the sum of the voltages of the batteries 611, 711, 61, 71, the relay 111 will operate. The current through the upper winding of relay 91 will exceed the current through the lower winding by an amount proportional to the voltage of the batteries 6E1 and 711 which is sufficient to cause relay 91 to operate.

Under these conditions therefore circuits may be traced as follows:

(1) Negative pole 5H1, contacts 40H, pole of battery 10H.

(2) Negative pole of battery 101, tripping coil 511, contacts 241, 251, 561, 571 to positive pole of battery 101.

Consequently circuit-breakers 41-11 and 111 will be tripped and the power line 111 out out of service. It will be noted that the circuit of the tripping coils 5112 and 512 open at contacts 54H and 55H and contacts 351 and 341 respectively, so that the power line 21-1 is not affected.

Secondly, with relays 81 and. 1.21 operated and 1211 unoperated the following circuits may be traced:

(1) Earth, contacts 4311. EI, negative pole of battery T11, battery '711, battery 611, contacts 3811, 3911, 4611, 4711, lower windings of re 91-1 and 1111, resistance 131-1 to earth.

(2) Earth, contacts 331, 321, 2 I, positive pole of battery 61, battery 61, batt ry 71, contacts 281, 291, lower windings of relays 91, and 111. resistance 131 to earth.

(3) Earth, contacts 421-1, negative pole of battery 711, battery 711, battery 611, contacts 3811, 3911, 461-1, 471-1, upper windings of relays 911 and 111-1, pilot wire .311, upper windings of relays 111 and 91, contacts 291, 231, negative pole of bat tery '71, battery '71, battery 61, contacts 221, 231, 321, 331 earth.

The current through the lower windings of relays 9H and 1111 will be proportional to the sum of the voltages of the batteries 6H and 7H and will be downwards in the lower winding of relay 91-1 and upwards in the lower winding of relay 1111. The current through the upper windings of relays 9H and 1111 will be proportional to the sure of the voltages of the batteries 61-1, 711, 61 and '71 of battery 19H, tripping coil 4111, 5211, 53H to positive 

